EGF stimulates cell growth and differentiation by binding to its receptor, EGFR. Human EGF is a 6-kDa protein with 53 amino acid residues and three intramolecular disulfide bonds. EGF (binding to EGFR) results in cellular proliferation, differentiation, and survival. Salivary EGF, which seems to be regulated by dietary inorganic iodine, also plays an important physiological role in the maintenance of oro-esophageal and gastric tissue integrity. The biological effects of salivary EGF include healing of oral and gastroesophageal ulcers, inhibition of gastric acid secretion, stimulation of DNA synthesis as well as mucosal protection from intraluminal injurious factors such as gastric acid, bile acids, pepsin, and trypsin and to physical, chemical and bacterial agents. Epidermal growth factor can be found in urine, saliva, milk, and plasma. The production of epidermal growth factor has been found to be stimulated by testosterone.